SAFETY EVALUATION AND PROTECTION MEASURES TO ADJACENT PIPELINES DURING DEEP EXCAVATION FOR METRO CONSTRUCTION

Three-dimensional finite element models with consideration of soil small strain stiffness characteristics and the thickness variation of soil layers were developed to investigate the effect of excavation of urban square of metro line 1 to adjacent pipelines in Xiamen city. The models were applied to investigate the safety of deep metro excavation. Protection measures based on the result of models were proposed. Then the computation results were compared with the real-time monitoring data to verify the model accuracy. Based on the models, the effect of pipeline material and diameter on deformation and endogenous force was analyzed. Different protection schemes for unsafe pipelines were proposed. The best alternatives were proposed by numerical simulation. It was shown that the influence of three-dimensional space-time effect on deformations and axial force of pipelines was significant. Taking safety threshold of relative angle and tensile stress as standards, the DN1000 was under unsafe condition. The protection measures of 2m×2m grouting reinforcement and two rows of prefabricated pipe pile near pipelines settlement were adopted.